Method of manufacturing mosaic electrodes



Oct. 10, 1939. A. ROSE 2,175,701

METHOD OF MANUFACTURING MOSAIC ELECTRODES Filed Sept. 50, 1937 INVENTOR. Al. BE T R055 6&0! ATTORNEY OFFE METHOD OF MANUFACTURING MOSAIC ELECTRODES Albert Rose, East Orange, N. 3., assignor. by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application September 30, 1937, Serial No. 166,540

2 Claims. (Cl. 250-275) My invention relates to a method of manufaction member suitable for use in practicing my inturmg multi-apertured electrodes of the doublevention,

sided mosaic type, such as are used in television Figure 2 is a greatly enlarged plan view of a transmitting and receiving tubes. portion of a mosaic electrode made in accord- 5 Many types of television transmitting and reance with my invention, and 5 ceiving tubes, such as disclosed by W. H. Hickok Figure 3 is a greatly enlarged cross-section of in United States Patent 2,047,369 July 14, 1936, a portion of the electrode shown in Figure 2. utilize a double-sided target or mosaic electrode Referring to Fig. 1, the foundation for the Which consists in general of a fine mesh foundamosaic electrode preferably consists of a fine wire tion screen of electrically conducting wire coated mesh screen i supported by a frame 2 which may 10 with a vitreous enamel, the interstices of the be of metal. All of the wires are coated with an mesh being filled with electrically conducting enamel or other vitreous insulating material metal plugs which are oxidized and treated with which has high electrical resistance properties. caesium to provide surfaces high in photoelec- As best shown in Fig. 2, all of the wires of the tric emission or surfaces having high secondary mesh are covered with the enamel 3 so that the 15 electron emission when bombarded by a beam of masses of metal or p s 4 an? held in p ac in high velocity electrons. the screen but are thoroughly insulated from the The manufacture of such electrodes entails metal of the screen by the enamel coating 3. considerable skill and experience as it is exceed- A greatly en a Cross-Section O is Strucingly difiicult to obtain an electrode having uniture is shown in Fig. 3. 20

form electrical characteristics over its effective In accordance with my invention I plug an insurface. It is necessary to fill the insulated sulated multi-apertured foundation member with interstices of the foundation screen with a metal a paste composed of finely divided metal powder or metal compound to form plugs which are of or readily-reducible metal compound and abinder uniform size and are mutually insulated one from which is solid at room temperatures, melts to a 25 another. Any satisfactory method of manufacthin liquid at temperatures somewhat above 40 ture should insure all of the holes being complete- C., and volatilizes at temperatures such that it 1y filled. Double-sided mosaic electrodes of this may be quickly removed at temperatures below type have been made by coating the foundation the sintering point of the metal powder. A prescreen with vitreous insulating enamel, the interferred way of practicing my method includes 3 stices being filled with a paste comprising finely heating both the material and the insulated divided metal powder or metal compound mixed foundation to a temperature around the melting with a semi-liquid binder consisting of rosin oil point of the binder, and applying the heated maslightly diluted with turpentine. It has been terial to the heated insulated foundation to com- 5 found, however, that by such amethod only about pletely fill the apertures or interstices with the 95% of the interstices are filled and, further, material. The insulated foundation is cleaned of that some of the filling is insecurely held within any excess material and the assembly is placed the interstices so that many of the metal plugs in a furnace to volatilize the binder and A. R. fall out during the subsequent steps of manusinter the powder to form the individually infacture. sulated metal plugs of the assembly. 40

It is an object of my invention to provide an The foundation may consist of a perforated improved method of manufacturing double-sided metal sheet, but is preferably a closely woven wire mosaic electrodes for use in television transmitmesh screen, and when such a screen is designed ting and receiving tubes which exhibit uniform for use in television transmitting and receiving 5 electrical characteristics over the entire effective tubes, it is desirable to provide a screen having surface. 150-200 or more wires per linear inch if the tube Another object of my invention is to provide a is to be suitable for reproducing a television method of manufacturing double-sided mosaic image in good detail. electrodes having minimum electrical leakage The choice of metal from which the founda- 5 and high photoelectron emissivity. tion screen is made is usually dictated by the These and other objects, features, and advanavailability of suitable insulating enamels. I pretages of my invention will appear from the folfer to use nickel wire screen which I have found lowing description taken in connection with the to possess certain advantages when coated with accompanying drawing in which: a vitreous enamel in which the percentages of Figure 1 is a plan View of one form of a foundaalkali and of silica are considerably high and the 55 percentage of boric anhydrid is lower than in the usual enamels. Such an enamel is described by John L. Gallup in his co-pending application Serial No. 115,192 filed September 10, 1936. This enamel is particularly advantageous because it is a poor solvent of metals, has high electrical resistance and has a thermal coefficient of expansion similar to that of nickel at the temperatures attained during manufacture and use. The nickel mesh screen i is rolled and treated with acid to increase the area of the holes or interstices as described by Hickok in his patent referred to above. Prior to enameling the nickel mesh I find it particularly advantageous to clean the nickel thoroughly, then oxidize it slightly by heating in air until it assumes a greenish color, probably due to a film of nickel monoxide, NiO. I then spray the mesh with the enamel ground to a particle size under two microns and held in suspension in either water or alcohol. The sprayed screen is then fired in a furnace at about 900 C. in air for a period of l to 2 minutes to fuse the enamel into a smooth glassy coating which completely covers all of the metal surface and adheres firmly to it. I prefer to build the enamel coating up to .a thickness of approximately 3 mils on the surface of the electrode and to a thickness of to 1 mil on the walls of the holes or interstices in the electrode by applying the enamel in several thin coats and firing the screen after each coat is applied. I find in this way that well-insulated screen electrodes highly suitable for the production of mosaic electrodoes for television transmitting or receiving tubes can be made with such a wire mesh screen.

Following the formation of the insulating coating on the electrode and in accordance with my invention, I fill the interstices thereof with finely divided metal powder, such as silver, or a readilyreducible metal compound such as silver oxide, which is mixed with a binder such as paraffine, preferably parafline having a melting point of around 50 C. The mixture may be made by melting a small quantity of paraffine and adding to it sufficient metal powder to produce a semi-fluid mass. The insulated foundation member is then heated to approximately the melting point of the binder, which in the example described is approximately 50 C., and the mixture applied by brushing it into the interstices with a camels hair brush. The interstices, however, may be filled in another way which I have found equally advantageous, which comprises coating the foundation member with a layer or film of a binder such as paraffine which is solid at room temperatures, supporting the foundation member on a smooth surface such as glass, heating the foundation to the melting point of the binder, sprinkling the powdered metal uniformly over the surface of the foundation member, and working the metal powder into intimate contact with the binder and into the interstices of the foundation by brushing the assembly with a camels hair brush. The foundation is cleaned of any excess binder and metal powder by maintaining it at a still lower temperature, approximately 35 C. in case the particular binder described is used, and gently rubbing it with a cloth. I have, however, found that the cleaning operation may be performed to advantage by sprinkling additional metal powder over the surface of the foundation and the filled interstices, after the foundation has cooled and the binder has solidified, and then rubbing the foundation with a cloth to remove the excess material. By the use of the latter cleaning method I have found that better separation of the metal plugs filling the interstices is obtained as the additional metal powder serves as an abrader to clean off any excess of the mixture deposited on the foundation between the interstices.

Following the cleaning operation the electrode is fired or baked by placing it in a furnace which is preferably at about 400 to 600 C., to volatilize the parafiine binder, which occurs at a temperature below the sintering point of the silver powder. The baking is continued for to 1 hour at 400 to 600 C. to sinter the silver powder and thereby form the metal plugs. The sintering of the silver powder provides a mosaic electrode wherein the plugs are electrically conducting and firmly held in the foundation so that the assembly will withstand normal mechanical shock during use without the metal plugs falling out of the interstices.

Mosaic electrodes made in accordance with my invention are particularly suitable for use in television transmitting and receiving tubes and may be sealed into the tube and photo-electrically photosensitized by oxidizing the silver plugs and treating the oxidized surface with caesium in the usual way. One method of photosensitizing the surface, which has proven satisfactory, is that disclosed by Sanford F. Essig in United States Patent 2,055,570 December 29, 1936.

My new method of manufacturing mosaic electrodes facilitates the assembly process in that the plugs are easily formed from the metal and binder which solidifies at room temperatures and are firmly held within the interstices prior to sintering. In addition, the use of a low melting point binder which is solid at room temperatures facilitates the formation of metallic plugs of uniform thickness in an insulated screen foundation. Further, in addition, the use of my invention provides a mosaic electrode wherein the interstices are completely filled, there being little likelihood of the plugs falling out of the interstices during subsequent operations in the manufacture of the electrode and during use. While I do not wish to be limited to any particular theory to explain why the plugs are more firmly held in the interstices or apertures of the foundation, I believe that the use of a low melting point binder allows the powdered material to flow into intimate contact with the coating of insulation so that when this material is sintered to form the metal plugs the material will not shrink away from the insulated Walls of the foundation. Thus the low melting point binder, when applied either prior to the application of the metal powder at which time the apertures are filled with the binder or when applied directly with the powdered material, causes the material to fiow into the interstices or apertures and become lodged very closely to the coating of insulation. This flowing of the binder or binder with the powdered material into the apertures may be due to capillary forces but the final result is a mosaic electrode in which the particles are firmly held and will not become dislodged during subsequent handling or use.

While I have described one modification of my invention utilizing a metal powder such as silver, and a low melting point binder which is solid at room temperatures, such as paraffine, it is evident that the invention is susceptible to other modifications utilizing metals other than silver and normally solid binders other than parafline. I therefore desire to be limited only to the extent necessitated by the prior art and by the appended claims,

I claim:

1. The process of fabricating mosaic electrodes from a wire mesh screen which comprises coating the exposed surface of said screen with an electrically insulating substance, filling the interstices of the screen with a mixture of paraffine and powdered material which when fired sinters and becomes electrically conducting while maintaining the screen at a temperature approximating the melting point of the parafiine to form individually separated plugs in the interstices of the screen, cooling the screen to solidify the parafiine, applying a quantity of the powdered material to each side of the prepared screen, mechanically working the powdered material into the plugs to remove the excess of the binder from the exposed surface of the insulated screen, and firing the electrode to volatilize the binder and sinter the powdered material.

2. The process of fabricating mosaic electrodes from a metallic apertured foundation member which comprises coating the exposed surface of said member with an electrically insulating substance, coating the insulated surface and filling the apertures of said foundation member with a film of low melting point binder, heating the foundation member to a temperature approximating the melting point of the binder, applying to the film of binder a powdered material which when fired sinters and becomes electrically conducting, mechanically working the powdered material into the apertures and into the binder in the apertures to form individually separated plugs in the apertures of the foundation member, cooling the screen to solidify the binder, applying an additional quantity of the powdered material to the surface of the prepared foundation member, mechanically working the additional powdered material into the plugs to remove the excess binder from the exposed surface of the insulated foundation, and firing the electrode to volatilize the binder and sinter the powdered material.

ALBERT ROSE. 

